Normal Vibrations, Potential Constants, and Vibrationmdash;Rotation Interaction Constants in Cyclobutane and Cyclobutanehyphen;d8

摘要

From the fundamental frequencies of cyclobutane and cyclobutanehyphen;d8as observed in infrared and Raman spectra, the potential constants and eigenvectors of the normal vibrations have been calculated for an assumed structure ofD4hsymmetry. When the available frequencies were too few in number to evaluate the constants of a given species in the generalD4hpotential system, appropriate nondiagonal constants were set equal to zero. From the potential constants the zeta constants of vibrationmdash;rotation interaction were computed forD4hspeciesEgandEu.TheEgconstants were found to be correct in magnitude but of opposite sign to the zetas suggested by the infrared band contours. The sign change is that to be expected if the actual structure isD2d(puckered ring), as was shown by Mills and Duncan for theD2dstructure of allene. The zeta constants and frequencies were therefore recalculated for speciesEofD2d. The calculated zetas agree well with the values expected from the band contours, and explain the unusual shapes of the bands at 749 cmmdash;1in cyclobutane and 556 cmmdash;1in cyclobutanehyphen;d8.